Some household dwellings are provided with underground septic systems having a series of leach trenches utilized for the leaching of liquids into the soil. Soil in its natural state is porous and durable. Unfortunately, at times organic matter can pass into the leach trenches from the septic tanks. The porosity of soil allows oxygen from the atmosphere to penetrate the soil pores and to aid in the decomposition of organic matter.
For the last 30 to 40 years, the disposal of household septic effluent, "on-lot", has been an increasingly attractive and environmentally necessary practice. Previously, and even today, in some areas of high density, slowly permeable soils, septic effluent is discharged into a road ditch or surface water drainage-way with little or no treatment. An alternative approach is to utilize the top 18 to 24 inches of soil to absorb and filter the effluent while allowing the natural bacterial community within the soil to breakdown hazardous solid wastes. This alternative approach is both cost effective and environmentally sound. It results in a naturally filtered supply of water entering the subterranean aquifers.
The efficiency of the "on-lot" septic absorption trench can be limited by reduction of soil porosity or rates of permeability caused by the current method of septic trench installation.
The current method of septic trench or leach trench installation, also known as ET or Evapotranspiration trenches, involves the use of very heavy equipment mounted on rubber tires. Most areas where leach trench systems are used experience wet weather conditions during the installation. The combination of wet soils and heavy concentrated loads, causes the pore spaces through which water must move to escape the trenches, to collapse or be crushed. The soil compaction can be as deep as 16 to 18 inches.
As a backhoe bucket is drawn through the soil, pressure is exerted laterally through the soil, again crushing the pore spaces through which water must move to evacuate the trench. It also glazes the walls of the trench, so as to further close pores.
Compaction, i.e., collapsing of pore space in the soil, has the effect of slowing the movement of water through the soil. In septic leach trenches this has the additional effect of maintaining nearly flooded conditions in the trenches, thereby preventing the entry of oxygen into the soil pores. The soil environment becomes an anaerobic environment. The bacterial community in this anaerobic condition produces small quantities of alcohol and formaldehyde, when digesting organic matter. Alcohol and formaldehyde are natural preservatives and stop the digestive process of the organic matter and even tend to preserve it in the undigested state.
A failing septic system, one which is not properly maintained by pumping accumulated solids, experiences a large deposition of organic matter in this anaerobic condition, the organic matter migrates to faces of the trench where it eventually plugs the pore spaces and essentially stops the movement of water into the soil. At this point septic effluent will bleed onto the surface of the ground, exposing the environment to untreated septic effluent and the high populations of bacteria and virus that exist therein.
Removing the organic matter has proven to be nearly impossible, without either resting the system for up to one year or replacing it with new trenches, or both. Resting the system requires either pumping the effluent continually, and removing the effluent from the property or installing new trenches into which the effluent is discharged for the duration of the resting cycle. Both options are expensive. Additionally, replacing the trenches has the identical limitation as that of the original trenches, they work until they become plugged with organic matter. State of the art at present is the replacement of an entire set of trenches and requires the availability of land of suitable topography and soil type and an area equal to the original system. Usually an area about 100 feet by 150 feet for a four bedroom home. Many times there simply is no replacement area due to topography, soil type or the size of the original land purchased. In this case, state of the art is off lot discharge after varying amounts of treatment of the effluent. This practice has severe limitations in more densely populated areas. Additionally, with this off-lot discharge practice, it has been found that a large percentage of home owners either do not repair the treatment systems or even shut them off when the cost of operation is realized. This can add significantly to pollution levels of surface water supplies.
A septic leach trench system which has been properly sized for soil type and has no restriction due to mechanically induced compaction, experiences an occasional flood of effluent, which is usually followed by a sufficient period of time for the effluent to leach out of the trench and establish an aerobic community of bacteria which reduce organic matter to carbon dioxide and water with some mineral residue. Complete digestion of organic matter results in an absence of material that might plug the pore space of the soil and slow or even stop water movement.
A method of restoring soil porosity and soil aeration to soils adjacent septic leach trenches is proposed. This method restores the original soil porosity and improves drainage of liquids from the trenches, encourages aeration and improves microbial degradation of accumulating organic matter. Benefits to be obtained are: reduction in the accumulation of organic matter and the decomposition of existing accumulations of organic matter thus unplugging the soil pore spaces within the soil. Unplugged pore spaces allow liquid to leach downward into the soil. This method of restoring soil porosity and soil aeration eliminates the need to replace failed leach trenches and will stop surface pollution of treated systems.